Apparatus for removing scale from pellet mills



1957 G. J. WEBSTER ETAL 2,8

APPARATUS FOR REMOVING SCALE FROMYPELLET MILLS Filed May 16; 1955 2 Sheets-Sheet 1 H PAIR FIG.

INVENTORS s..1. WEBSTER BY J.S.MART|NEZV MAVW.

AT TORNE-YS G. J. WEBSTER ET AL 2,812,541

Nov. 12, 1957 APPARATUS FOR REMOVING SCALE FROM PELLET MILLS 2 Sheets-Sheet 2 Filed May 16, 1955 INVENTORS G.J.WEBSTER J.S. MARTINEZ ATTORNEYS APPARATUS FOR REMOVING. SCALE FROM PELLET MILLS George J. Webster and Jesus S. Martinez, Burger, Tex., assignors to Phillips Petroleum Company, a corporation of Delaware Application May 16, 1955, Serial No. 508,577

4 Claims. (Cl. 18-1) This invention relates .to improved pelleting mills for pelleting powdered materials such as carbon black. A specific aspect of the invention pertains to an apparatus for preventing and removing scale from the inside 'wall of a pelleting mill.

It is conventional to pelletize various powdered materials by rolling or tumbling the same in a cylindrical shell or drum rotating with its axis in a horizontal position. Carbon black is commonly pelleted in this manner to convert loose black, having a density of 3-4 pounds per cubic foot, into a pelleted and dustless product having a density of 21-24 pounds per cubic foot, depending upon the type of black. Metal oxides in powdered form, suitable for catalysts, are also pelleted by the method described herein. A conventional pellet mill comprises a cylindrical drum 6 or 8 feet in diameter by 48 feet in length mounted on a four-point trunnion suspension system. The mill is rotated by an electric motor speedreducer pinion drive which meshes with a girth gear mounted around the periphery of the mill. Weir adjustment plates are installed in the outlet end of the mill to permit adjustment of the bed depth and thereby control the character of the pellets. Loose black is fed to the opposite end of the mill by screw type conveyors supported by a center beam which extends axially through the mill. Scrapers for removing mill scale are also mounted on the center beam.

During the pelleting process, as conventionally practiced, loose black and carbon black dust tend to adhere to the inside surface of the mill forming a layer of scale which eventually seriously hinders the operation of the mill unless the same is removed.

The current method for removing this scale is by means of scrapers attached to a central axial beam. The scrapers are of two general types, rigid and spring loaded. This latter type is necessary in those mills equipped with pneumatic tires, because of the excessive lateral movement of the drum. Trunnion equipped mills are fitted with rigid scrapers. Both types present disadvantages which have been magnified since the introduction of semi-wet I pelleting.

The spring loaded scrapers exert a wiping action, rather than a true scraping action. They therefore tend to back 011 from the mill shell until the springs exert suflicient force to prevent further movement. In a dry mill this distance is in the range of /2 to 1 inch; however, in a semi-wet mill it increases to the range of 4 to 6 inches. With a pellet bed depth in these mills of about 8 inches and with a scale thickness of 4 inches the mills capacity is decreased about 60 percent. Heavier springs have been tried without too much success, since they cause excessive torque on the center beam and scraper arms. There has been a noticeable increase in necessary scraper repairs, and in two instances of record holes have actually been worn in mill shells. These stronger springs also increase the load on drive motors.

In the mills equipped with rigid scrapers, an entirely diflerent form of trouble has been encountered. The

nited States Patent scrapers in these mills are adjusted to provide a one-half inch clearance at the closest point. Some of the mills are as much as three inches out-of-round, so that the scale thickness varies in these mills from /2 to 3 /2 inches. Since the rigid scrapers do not contact the scale until it builds up to a suflicient thickness, a relatively Weak bond is formed on the mill shell. In the 8-foot diameter mills this is particularly troublesome, because of the wider radius arch at the top. The scale has always broken loose from these mills in large quantities frequently causing mills to revert entirely to loose black. This situation has been aggravated by semi-wet pelleting for some unknown reason.

Another obvious disadvantage common to both types of scrapers is that they add weight to the already overloaded center beam. Actually in'some of the mills, feed screws are so arranged to make possible complete elimination of the center beam if the scrapers are removed, the sole purpose of the beam being to support the scrapers.

The principal object of the invention is to provide an improved pelleting mill for pelleting powdered materials, such as carbon black. Another object is to provide an improved pelleting mill which prevents formation of scale of substantial thickness on the inside of the mill. Another object of the invention is to eliminate the need for scale scrapers on the inside of a pellet mill together with all of the disadvantages of this type of equipment. It is also an object of the invention to provide a pellet mill which does not require an axial support beam. Other objects of the invention will become apparent from a consideration of the accompanying disclosure.

We have devised a pellet mill which continuously r emoves mill scale by an entirely difierent principle than the scraper system utilizes. The invention provides for the removal of the scrapers and the substitution of a flexible liner attached at spaced points to the inside of the pellet mill. A group of rubber or other flexible panels are attached to the inside surface of the pellet mill shell and one or more ports in the mill shell are located behind each of these panels. Theseports prevent vacuum formation between the liner and the mill shell and, in certain embodiments of the invention, provide a housing for mechanical flexers which are used to urge the liner away from the mill wall around the ports so as to cause or initiate sagging of the various sections of the liner passing through the upper portion of the arc of rotation of the mill whereby the same sag away from the shelland thereby disengage any scale and/ or loose material which has been deposited on the liner.

In another embodiment the ports are utilized for the introduction of compressed gas, such as compressed air, between the various liner segments and the opposite shell portion so as to positively flex the lining segments and disengage powdered material and/or scale from the inside surface of the flexible liner.

The flexible liner may be fabricated from rubber or other impervious flexible sheet material and is sealed at all joints so as to prevent the infiltration of powdered material between the liner and the mill shell. The rubber material may be impregnated on fabric of woven or cord material. It is also feasible to utilize various fabrics which are rendered impervious by plastics, resins, etc. Tightly woven fiber glass in the form of cloth or fabric may be rendered impervious by various coatings and fillersknown in the art and utilized to fabricate the liner of the invention. The liner material selected must have the capacity to withstand temperatures and other operating conditions obtaining in the particular pelleting process in which it is applied.

More complete understanding of the invention may be had by reference to the accompanying diagrammatic drawing of which Figure l is a transverse cross section of a pellet mill utilizing one embodiment of the invention;

Figure 2 is a transverse cross section of a similar pellet mill illustrating another embodiment of the invention; and Figure 3 is a longitudinal cross section of a pellet mill similar to that of Figures 1 and 2 showing a preferred arrangement of the liner segments.

Referring to Figure l, a pellet mill comprises a shell or drum 11 mounted on a wheel and axle arrangement 12 for rotation in conventional manner as described more fully in connection with Figure 3. The mill encloses a bed of pellets and powdered material 13. Mill it) isprovided with a flexible liner 14 which is directly attached to shell 11 at spaced apart points or areas by means of strips 16 which extend longitudinally from end to end of the mill thereby forming a number of liner segments 18. The mill liner may be made in whole or in parts corresponding to segments 18; however, it is preferable to construct the liner in segments and attach the same to the mill, as shown, by sealed joints provided by strips 16 which have rounded edges to reduce wear on the liner in the area of attachment and to minimize any deleterious effect on pelleting which the strips may tend to produce. Strips 16 may be fabricated of inflexible or rigid materials, such as metal and wood, or of flexible material, such as rubberized fabric comparable to that found in automobile tires. The strips are attached to the inside wall of the mill by bolts, screws, or other suitable fastening means which does not protrude into the mill beyond the strips suificient to deleteriously effect the pelleting process. Segments 13 may be of any suitable size which permits sagging of the liner material from strip to strip without causing excessive strain on the liner material. The flexible panels must be made of such a size and thickness that they retain the inside contour of the mill when in the lower half of the mill so as to avoid interfering with the formation of pellets by tumbling and rolling therein. Segments 1 foot to 6 feet in width are found operable with satisfactory results in pellet mills having a diameter of 6-8 feet and it is preferred to construct the liner arrangement with segments in the range of 25 feet in width. It is not essential that segments 18 extend uninterruptedly from end to end of the mill as these segments may be of short lengths of one to several feet, as shown in Figure 3. It is also feasible to attach the liner at spaced points both longitudinally and circumferentially of shell 11 by suitable fastening means, such as carriage bolts extending through round washers of rigid or flexible material superimposed on the liner. In this type of construction the liner can be formed in one piece or in large sections with the joints between sections sealed by strips as described above.

The mill shell is provided with ports 2-0 opposite each liner segment and preferably centrally thereof to provide for the introduction of air or other gas between the liner segment and the opposite section of the mill shell. These ports 20 are arranged in line on a circumference of the mill in order that they may be fed compressed gas from a single source such as cup 22 which is positioned in engaging relation with an upper section of the mill and rides on a smooth circumferential band 24 provided for this purpose. Cup 22 maintains a seal with band 24 by means of suitable packing material 25 enclosed by a U-shaned retainer 28 having a rectangular or circular contour. Cup 22 is provided with brackets 30 against which compression springs 3?. apply pressure so as to maintain a proper seal. Springs 32 are held in place by suitable telescoping expansion rods 34 one end of which is connected with a support beam 35 and the other end with bracket 39. A gas line 36 leads into cup 22 and is connected with a pressure regulator '37 which is, in turn. fed by a high pressure line 38. For economic reasons, air is the preferred gas for use in operating the system disclosed in Figure l.

The operation of the device of Figure 1 involves rotating mill 10 so that powdered material in bed 13 is carried up the side of the mill and rolled or tumbled back toward the bottom of the mill in conventional manner. As each port 20 passes under cup 22, air is forced through the port so as to separate the lining in segment 18 from the opposite portion of the shell 11 thereby flexing the liner material and disengaging any scale that has begun to form on the liner segment. As port 20 passes from under cup 22, the compressed air between segment 13 and the shell passes to atmosphere and does not interfere with the return of the liner segment to contact with the mill shell. Pressure regulator 37 is set to provide only sufficient pressure to flex each segment without subjecting the liner to unnecessary strain. Pressures of the order of 0.5 to 2 p. s. i. g. are satisfactory. In this manner sections 18 move in progression under gas supply cup 22 and are inwardly flexed so as to prevent and/ or remove scale which tends to form on the inside of the mill.

Referring to Figure 2, mill 10 which is similar to that of Figure 1 (corresponding parts being correspondingly numbered), provides another embodiment of the invention which diiiers from the embodiment shown in Figure l principally in the mechanical flexing means for effecting separation of liner segment 18 from the opposing section of the mill shell. The liner in this figure is attached to the shell by means of carriage bolts 40 secured by nuts 42 on the outside of the shell. The convex head 43 of bolts 40 firmly attaches strip 16 at spaced points to the liner segment which in turn is attached to the inside of the shell. as shown. The mechanical flexing device 49 comprises a rod or stem 45 extending through port 20 and provided with a disk 46 on its inner end, which is larger than port 20. Breather holes 47 are provided in the housing of device 49. A compression spring 48 engages the shell of the mill around the port and also engages a fixed disk or transverse member 50 which is detachably attached to rod 45. A bracket 52 is attached to shell 11 and provides a guide and slidable bearing for rod 45. Disk 4-6 may be made perforate so as not to obstruct the ingress and egress of air through port 20 to and from the area between the mill liner and the shell.

The device for actuating mechanical flexers 49 comprises an oblique plate 54 which is supported from an overhead support rod or beam 56 by means of braces 58. Actuating plate 54 is fixed above the upper side of the mill so that the more distant edge 60 is slightly farther from the mill shell than the outer end of rod 45 when the latter is in normal position; and the closest point (area 61) of plate 54 is a distance from the mill shorter than the normal projection of rod 45 from the mill. Thus, as the mill is rotated in a counterclockwise direc tion, as shown, the outer ends of rods 45 progressively pass under actuating plate 54 which forces disk 46 inwardly so as to urge liner segment 18 away from the opposing shell section and effect sagging and flexing of the iner segment directly under the particular flexer assembly being actuated, thereby preventing and/ or removing scale from the liner as described in connection with Figure 1. As the flexer assembly progressively rotates past actuating plate 54 spring 48 gradually returns disk 4-6 to normal position against the inside of the. shell thereby permitting the return of liner segment 18, associated with this flexer, to return to its normal position in contact with mill shell 11 when this liner segment passes the horizontal diameter of the mill. It is feasible and desirable to provide a recess on the inside of mill shell 1i around each port to receive disk 46 thereby avoiding any extension of this disk beyond the inner contour of the mill shell.

Referring to Figure 3, mill 10, which is similar to the mills illustrated in Figures 1 and 2, is closed by a feed end plate 64 having an axial opening 66 therein for introduction of powdered material to the mill by conveyor means not shown. The mill is closed at the opposite end by delivery end plate 68 which is provided with weir openin gs 69 for egress of finished pellets from the mill as the mill rotates. The mill is supported by wheel and axle supports 12 which operate in trunnions not shown. A girth gear 7% encircles the mill shell and provides a means of rotation of the mill by a pinion drive not shown attached to a suitable drive means in conventional manner.

The mill liner is formed in a series of rectangular segments 18 which are attached at the edges by means of longitudinal strips 16 and circumferential strips 72 secured to the mill by bolts or screws 43. The liner arrangement shown provides three series of circumferentially arranged segments 18 having centrally positioned ports and mechanical flexers 49 so that all of the flexers in each series are operated by a single actuating plate 54. It is also feasible to arrange ports 20, together with their cooperating mechanical flexers, in a spiral or helical pattern so that the same are operated in the order in which they appear in the helical pattern.

The liner of the invention in its various embodiments is operable satisfactorily without positive means for urging the liner away from the shell, air being free to enter ports 20 and the weight of the liner segments being sufficient, at least under some operating conditions, to cause sagging and flexing of the liner so as to prevent scale build-up. However, the means disclosed herein for positively separating the liner from the shell is preferred in order to avoid eventual sticking of the liner to the shell under continuous usage. The device may be operated to advantage with breather holes or ports in the shell in addition to the ports housing the fiexers or the ports through which compressed gas is forced. While the drawing shows cups 22 and flexer actuators 54 positioned adjacent the upper end of the vertical diameter of the mill, these elements may be positioned adjacent any section of the upper half of the shell but the uppermost position is preferred.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. A pelleting mill comprising in combination an elongated closed cylindrical shell having a feed inlet at one end and a pellet outlet at the other, adapted to be rotated with its axis in a substantially horizontal position; a flexible imperforate liner on the inner Wall of said shell attached thereto by circumferential spaced-apart strips and by longitudinal spaced-apart strips forming said liner into rectangular flexible sealed sections; ports in said shell providing an opening into the area behind each said section, said ports being aligned circumferentially in series corresponding With said sections; an inverted stationary cup aligned with each series of ports and adapted to ride said shell in sealed relation therewith when each port passes under same in the upper arc of rotation; and a port in each said cup for injecting pressurizing gas.

2. The apparatus of claim 1 including means for forcing compressed gas through the ports in said cups.

3. A pellet mill comprising in combination an elongated closed cylindrical shell having feed inlet means at one end and feed outlet means at the other end, adapted to be rotated about its axis when in a substantially horizontal position; a flexible imperforate liner on the inner wall of said shell attached thereto by laterally spaced-apart overlay strips extending longitudinally of said shell from end to end and by circumferential overlay strips at each end of said shell and liner and at least one intermediate circumference, said strips being provided with fastening means passing from said strips into said shell at spaced intervals, thereby forming said liner into several rectangular flexible sections, said liner being sealed against infiltration of powdered material between said shell and said liner from within said mill; a series of ports in said shell comprising at least one port opposite each of said sections for introducing gas between said liner and said shell to assist in separation thereof, each port in a series being in line on a circumference of said shell; a smooth band on the exterior of said mill along said circumference through which said ports extend; an inverted cup held in sealed engagement with said band in the upper section thereof; and a gas feed line connected with said cup for introducing gas through said ports as same are rotated under said cup.

4. The mill of claim 3 including means for holding each said cup in sealed engagement with said band comprising a pair of springs in compression between a fixed support and said cup urging said cup toward the axis of said mill.

References Cited in the file of this patent UNITED STATES PATENTS Re. 18,597 Shimin Sept. 13, 1932 2,603,832 Clark et al. July 22, 1952 2,711,557 Russell June 28, 1955 

